Current cancer therapy is often insufficient to completely eradicate disease and is frequently complicated by unwanted side-effects. This proposal seeks to devise a novel treatment strategy using alveolar rhabdomyosarcoma as a model system by exploiting genetic rearrangement which underly many cancers. Alveolar rhabdomyosarcoma, which is highly resistant to conventional therapy, contains a translocation between chromosomes 2 and 13 that encodes a chimeric transcription factor, PAX3-FKHR. PAX3-FKHR is a strong transcriptional activator of promoters containing PAX3 DNA-binding sites and is expressed only in alveolar rhabdomyosarcoma cells. Such a promoter has been constructed that is transactivated by PAX3-FKHR, is active in cells containing t(2;13), but is inactive or repressed in other cells types. Regulated expression of a fragment from the Corynebacterium diphtheria bacterial toxin gene by this promoter will be tested for specific cytotoxicity of alveolar rhabdomyosarcoma cells in culture using transient transfection conditions which achieve greater than 99 % gene transfer. The utility of selectively eliminating tumor cells from a mixed cell population as a model for autologous bone marrow purging will also be tested. Conditions for in vivo gene transfer to human xenografted tumor cells in a mouse model using lipofection and lipofection augmented by concomitant adenovirus infection will be explored. Toxic side-effects of these methods of in vivo gene transfer in mice will be monitored and minimized. Finally, the feasibility of treating cancer with this novel gene-based strategy will be assessed by monitoring tumor growth in treated mice. This strategy will serve as a paradigm for genetic therapy of other tumors such as Ewing~s sarcoma, liposarcoma, and some forms of leukemia which express analogous chimeric transcription factors.